Filament support



May 7, 1935.

' J. M CULLOUGH FILAMENfI SUPPORT Filed June 27, 1934 m m W m z m mu 1M q W 1 m .m MAW l in 1 D Z fi l P g z Patented May 7, 1935 PATENT mm FILAMENT SUPPORT JaclrMcCullough, San Bruno, Califi, assignor to Heint'z & Kaufman, Ltd., San Francisco, Calif.,

v a corporation of Nevada Application June 27, 1934, serial no. 132543 Claims. (01. 25o-'27;5)

invention relates to filament supports for thermionic tubes or thelike, and more particularly to a filament support which will not impart a turning stress to the filament supported. I

The principal object of my invention is to provide a support for a V-eshape'd filament, which when heated will have no tendency'to twist the filament out of itsnorm'al plane; another object of my invention is to provide a dependable filamentrsupport for an inverted v-shape'd filament placed relatively close to a cooperating electrode; andpa. still further object of my invention is to provide an improved filament support for thermionic tubes and the like, which is particularly 151 adaptable for use with closeelectrode spacings.

Other objectsof. my invention will be apparentor will be specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment ofthe invention herein described, as various'forms may be adopted within the scope of the claims. 7

In the drawing, Figure 1 is a longitudinal view partly in section and partly in elevation showing my invention as applied to a thermionic tube having parallel plate-like electrodes positioned on opposite sides of the filament.

Figure 2 is a cross-sectional view taken dicated by the line 2-2 in Figure 1.

It is quite customary in the art to utilize inverted V-filaments in designing thermionic tubes of various kinds, and it is likewise quite customary to support the bight bend of the V by means of a coil spring attached at one end to the envelope, and having at the other end a hook adapted to engage the bight of the filament. Such an arrangement is satisfactory when electrode spacings are relatively large. But when the filament is placed relatively close to a cooperating electrode it is not satisfactory, as there is a turning stress 40 imparted to the bight of the filament because of the fact that the spring when heated or cooled tends to coil or uncoil. One end of the spring being fixed, and the other end being attached to the bight of the filament, such coiling or uncoiling twists the filament. and if close spacing is used, will in many cases cause the filament to contact the adjacent cooperating electrode.

It has also been found that after a tube has been assembled and is subsequently processed that there is a large initial twist of the spring due to the first application of heat during the processing wherein the rotation of the filament bight may 7 be as high as a quarter turn. Efiorts are made to compensate for this initial twist of the spring by 66 assembling the tube by giving an opposite twist as into the filament bight so that when the adjustment twist of the coilspring occurs', the filament bight will be approximately'intheproper position. i This procedure, however, is not uniformlysa'tisfactory in that some springs will twist more than others and at best a mere approximation oi the" proper location can be obtained. Furthermore; such an arrangement can hardly takecar'e' of the smaller subsequent twisting strains which occur in the spring every time the finished tube is placed in and out of operation. e i v I have provided an improved filament support in the form of a coil spring which avoids the diificulties heretoforei encountcred, and which does not impart any twisting moments to the bight of the filament whenthe'tube is heated.

In broad terms my filament'support comprises a coil spring attached at one end tothe"envelope and at the other end to the bight of an inverted V-shaped filament, the spring being divided into two, preferably equal size, portionswound in opposite directions.

I have chosen for the purposes of illustration a particular form of thermionic tube in-which the advantages of my improved filament support are particularly apparent. I do not, however, wish" to be limited to any particular type of tube, as it-is obvious that the invention may be embodied in any form of device wherein it is desired to maintain a filamentary cathodein position.

An envelope I is provided with a reentrant stem 2 at one end and a support tube 3 at the other. Cathode leads 4 are sealed through the press 5 of the stem 2 and provide the basal support for a pair of inverted V-shaped filaments 6-6. A filament support frame 1 is fastened by means of a clamp 8 to the support tube 3, this frame having a support bar 9 attached thereon and closed across the end by a guide-bar ID. A pair of filament support springs ll-JI are fastened at one end to the support bar 9 and pass through apertures in the guide-bar I 0 to an end-hook l2 engaging the bight l3 of the filament.

A planar anode l4 supported by an anode support l5 sealed to an anode arm I6 is positioned on one side of the filament, anda control electrode ll supported by a control support J8 sealed through a control electrode arm I!) is positioned on the other side of the filament. Connection caps 20 and 2| are placed on the outside of the arms and serve to makeconnection to their respective electrodes.

I prefer to provide the stem-end of the tube with a base 22 having thereon cathode connections 23 which are connected inside of the base to the cathode lead 4. I prefer to connect the two filaments in parallel.

In the type of tube shown it is highly desirable to have the control electrode l1 positioned as close to the filament as possible. When this spacing is made close it is quite obvious that any twisting of the bights l3 of the filament will cause the filament to short against the control electrode. It is also quite obvious that the same condition obtains if the filament were being used in the conventional type of grid which surrounds the filament on both sides, if such a grid were to be placed to closely surround the filament.

I avoid twisting stresses by my particular con-.

struction of the filament support springs ll| l. I wind one portion of the spring, in this case the upper portion 25, in one direction for substantially half of the length of the spring. I then reverse the direction and wind the lower portion 26 in the opposite direction.

Considering this spring as a whole, the upper end is fixed to the support-bar 9 and the lower end passes through apertures in the guide-bar I0 to engage thebight of the filament. It is quite obvious that there will be some resistance toward turning-offered to the lower end of the spring by the'stiffness of the-filament itself and by the fact that the springs pass through the apertures in the guide-bar. It will also be obvious that at the point 21 where the spring reverses its direction, there will be no resistance to turning whatsoever. Consequently when thespring is heated and both portions of the, spring tend to expand and thereby rotate, the two ends of the spring do not turn but the motion is all at the point 21. I am thus able to assemble a thermionic tube embodying my invention by carefully adjusting the filaments to lie in the plane wherein I eventually desire them. Thereafter during the processing or use of the tube any twisting moments developed due to the heating or cooling of, the tube simply changesthe position of the point 21 and does not tend to twist the bight of the fila- ;ment 24. As any such twisting of the point 21 will have no effect on the position of the elements, I am able to obtain a much better. and a much finer adjustment of the position of the filament than by the use of a coil spring wherein all the turns proceed in the same direction.

The adaptation of my invention to tubes of other types, sizes and kinds, or to other devices wherein like results are desired, will be immediately apparent to those skilled in the art.

I claim:

1. In combination, a thermionic tube comprising an envelope containing an electrode having a substantially planar face, a filamentary cathode occupying a plane adjacent said face, and a coil spring supporting said cathode, said spring having oppositely wound portions of substantially equal length.

2. In combination, a thermionic tube comprising an envelope containing an electrode having a substantially planar face, an inverted V-shaped filament occupying a plane parallel to and adjacent said face, and a coil spring supporting the bight of said filament, said spring having oppositely wound portions of substantially equal length.

3. In combination, a thermionic tube comprising an envelope containing an. electrode having a substantially planar face, an inverted V-shaped filament occupying a plane parallel to and adjacent said face, and a coil spring fixed at one end to said envelope, the other end engaging the bight of said filament, the intermediate coiled portion being divided into oppositely wound portions of substantially equal length.

4. In combination, a thermionic tube comprising an envelope containing an electrode having a substantially planar face, an inverted V-shaped filament occupying a plane parallel to and adjacent said face, and a coil spring fixed at one end to said envelope, the other end engaging the bight of said filament, the intermediate coiled portion being oppositely wound to create equal and opposing turning stresses when subjected to heat.

5. In combination with an envelope containing an inverted V-shaped filament occupying a plane, means for maintaining the position of said plane comprising a coil spring depending from said envelope and engaging the bight of said filament, said spring having oppositely wound portions connected to prevent rotation of said bight when said spring is heated.

JACK MCCULLOUGH. 

